I'm sure they're sophisticated enough to be able to render the website properly w/ JS. Search engines aren't just regular simple crawlers (not that I condone the use of JS for what could have been a simple static HTML & CSS page given how minimal it is).

Google started rendering pages before indexing a while back because of this...so generally it's ok from an indexing perspective (assuming you still have working URLs that can also be loaded in the same way for all your linked-to content).